During the past five years, many manufacturers of high performance liquid chromatography (HPLC) columns have focused on improving stationary-phase stability and reproducibility, Improved column stability - both chemical and thermal - offers new advantages, such as decreased analysis time and new methods of selectivity optimization. More stable HPLC packing materials have been achieved through advances in silane chemistry; however, the greatest improvements in stability have resulted from the use of alternative nonsilica supports such as synthetic organic polymers, alumina, and zirconia. In this article, the authors describe their use of various test solutes to compare the efficiency, selectivity, and hydrophobic retention mechanisms of five commercially available HPLC columns based on silica, alumina, zirconia, and polystyrene cross-linked with divinylbenzene (PS-DVB).